Measurement of Thomson-scattering spectra with continuous angular resolution (invited)

Area of Science:

• Plasma Physics
• Laser-Induced Plasmas
• Spectroscopy

Background:

• Characterizing high-energy plasmas is crucial for fusion energy research.
• Understanding electron velocity distribution functions (EVDFs) is key to validating plasma models.
• Existing diagnostics have limitations in probing EVDFs over wide ranges.

Purpose of the Study:

• To develop and implement a novel Thomson-scattering diagnostic for detailed plasma characterization.
• To enable measurements of EVDFs without prior assumptions on their mathematical form.
• To probe a wide range of plasma frequencies and wave vectors in laser-produced plasmas.

Main Methods:

• A Thomson-scattering diagnostic with 120° continuous angular resolution was designed and built.
• Key components include a reflective objective, spatial filter, cylindrical optics, spectrometer, and gated camera.
• Spectra of scattered light were analyzed as a function of emission angle and wavelength.

Main Results:

• The diagnostic achieved 0.8-nm spectral and 1° angular resolution.
• It successfully measured EVDF properties in gas-jet plasmas heated by inverse bremsstrahlung.
• Data provided critical constraints for plasma physics models.

Conclusions:

• The novel diagnostic offers efficient probing of plasma parameters over broad ranges.
• It enables accurate, assumption-free measurements of EVDFs.
• This advancement is vital for interpreting experimental data and refining plasma physics models.